This invention relates to a thin film magnetic head and, more particularly, to a thin film magnetic head with improved recording and reproduction characteristics.
A thin film magnetic head is used as recording and reproducing means in a magnetic disk device. A prior art magnetic head used for a magnetic disk device is illustrated in FIGS. 2a, 2b and 2c. FIG. 2a is a front view, FIG. 2b is a view taken along arrows A--A in FIG. 2a and FIG. 2c is a view taken along arrows B--B in FIG. 2a. In this prior art magnetic head, the conducting coil is made in three layers.
This thin film magnetic head 1 includes a clean, mirror-surface slider substrate 10 which is made of, e.g., an Al.sub.2 O.sub.3 --TiC system ceramic plate. On this substrate 10 is deposited, by the sputtering method, a undercoat layer 12 of SiO.sub.2, Al.sub.2 O.sub.3 or the like of 10 and several .mu.m thickness. A lower magnetic layer 14 is provided on the undercoat layer 12 by electroplating, for example, A magnetic gap layer 16 is deposited by sputtering on the lower magnetic layer 14 to form a magnetic gap 17. The magnetic gap layer 16 is made, for example, of SiO.sub.2, Al.sub.2 O.sub.3 or the like as the protective layer 12.
A first insulating layer 18 is provided on the magnetic gap layer 16. A positive type photoresist is normally used as the insulating layer which is cured to a stable state by heating. On the first insulating layer 18 is formed a first coil layer 20 of a thickness of several .mu.m by copper electroplating. On the first coil layer 20 are sequentially formed, by the same methods, a second insulating layer 22, a second coil layer 24, a third insulating layer 26, a third coil layer 28 and a fourth insulating layer 30.
On the fourth insulating layer 30 is formed an upper magnetic layer 32 by electroplating. The rear portion of the upper magnetic layer 32 opposite to a pole portion is in contact with the lower magnetic layer 14. A protective layer 34 of SiO.sub.2, Al.sub.2 O.sub.3 or the like is deposited by sputtering on the upper magnetic layer 32 to cover the entire upper magnetic layer 32.
In the prior art thin film magnetic head, the exposed foremost end surface of the pole portion (leading pole 36 and trailing pole 38) of the upper and lower magnetic layers 14 and 32 is, as shown in FIG. 2c, formed on a normal line with respect to the direction of relative movement of a recording medium. This edge shape, however, causes a distortion called undershoot in a magnetizing inverting portion of a reproduced signal as shown in FIG. 3 and this undershoot causes a reading error.
It is, therefore, a first object of the invention to overcome this problem and provide a thin film magnetic head with reduced undershoot and improved reproduction characteristics.
In the prior art thin film magnetic head 1, there is also the problem that its recording characteristics are adversely affected by magnetic saturation of the pole portion. The state of magnetic saturation of the pole portion in the thin film magnetic head 1 in relation to the magnitude of write current is shown in FIGS. 15a, 15b and 15c and described in Table 1.
TABLE 1 ______________________________________ FIG. 15a FIG. 15b FIG. 15c ______________________________________ write current small medium large magnetic satu- none immediately be- significant ration of pole fore saturation saturation write magnetic too weak strong and strong magnetic field to write sharp magnetic field produced field produced in broad range density of -- high low recording ______________________________________
In the prior art thin film magnetic head 1, the phenomena shown in FIGS. 15a and 15c are produced unless the write current is properly adjusted. It is however extremely difficult to manufacture a magnetic head which can obtain a proper magnetic field as shown in FIG. 15b and it is also difficult to adjust a throat height (FIG. 2a) for this purpose with the result that production efficiency of the magnetic head is held at a low level.
It is therefore a second object of the invention to provide a thin film magnetic head with improved recording characteristics.